Scrap shredding machines are known, in particular for automobile bodies, for example, from the international application WO-A-2009/156432.
Normally, shredding machines operate in the presence of nebulized water in order to limit the risk of explosions due to the possible presence of flammable materials in the gas tanks of the car to be scrapped.
There are two streams exiting from the shredding and sorter machines, a primary one, from the shredder, consisting of air and powders generated by the crushing of the materials entering the machine, and a secondary one, which is coarser, coming from the air separator downstream of the shredder, which processes the heavier material, that is, in which the crushed material is progressively “selected” until the most accurate separation possible is obtained (ferrous, non-ferrous and “fluff”).
The need to control and reduce emissions into the atmosphere coming from such shredding machines is known, both with regard to the content of powders and with regard to the total content of organic carbon (TOC—Total Organic Carbon).
However, there are shredding machines which, operating in areas without strict legislation, do not provide any processing of the air exiting from the machine.
On the other hand, for shredding machines installed in countries with more environmentally friendly legislation, the primary stream of air has to be processed in order to reduce the content of fine powders and TOC to below the desired limits, just as the secondary stream coming from the classification of the heavy or coarse material exiting from the shredding machine is processed.
In such cases, the primary stream is normally processed using a humidity purifier or a scrubber. The scrubber provides to separate the powders, but it is of limited efficiency for damping down the volatile organic substances and hence the TOC.
Document US-A-2005/028672 shows a filtering apparatus to remove pollutants and contaminants from a stream of exhaust gas originating from an incinerator, after it has passed through a scrubber, which provides, in series, a heating chamber, and adsorption chamber using active carbons and a filtering chamber with layers of HEPA filters. In particular, only the exhaust stream exiting from the scrubber is fed to the heating chamber.
Document JP-A-2001272023 shows a method to remove powders, HCl, SOx, NOx, dioxins and other pollutants from a stream of exhaust gas coming from an incinerator. The method provides the use of a cyclone unit, an electric powder collector and a scrubber. The powder of the stream to be processed is recovered by means of the cyclone unit and the electric powder collector, while SOx, NOx, are removed from the gas using the scrubber. After the scrubber, a heat exchanger is provided to which all the exhaust stream coming from the scrubber is exclusively fed, to be heated to 100° C.-200° C. Active carbon powder, which absorbs the dangerous components present in the gas, is then added to the heated stream.
However, both US-A-2005/028672 and JP-A-2001272023, since they are intended for processing exhaust gases from incinerators, and not gas coming from scrap shredding machines which have the risk of exploding as explained above, completely neglect this problem, providing, in a traditional way, the passage of the exhaust gases directly through a chamber or other direct heating device. As a consequence, these known solutions are not suitable for the purposes of the present invention.
Purpose of the present invention is to obtain a plant, and to perfect a relative method, for de-powdering downstream of a shredder machine which reduces and controls atmospheric emissions of powder and total organic carbon content.
A further purpose is that the plant, and the connected method, of the present invention are safe and reliable, avoiding the risk of exhaust gas explosions deriving from the shredding machines upstream.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.